Short-term fasting may improve health

After years of fasting, the Buddha’s “legs were like bamboo sticks, his backbone was like a rope, his chest was like an incomplete roof of a house, his eyes sank right inside, like stones in a deep well,” according to one account. The Buddha didn’t get what he wanted from this extreme fasting—enlightenment—but a new study suggests that a diet that replicates some effects of milder deprivation may not only lower your weight but also confer other benefits. Researchers report that following the diet for just 5 days a month improves several measures of health, including reducing the risk of developing cardiovascular disease.

Eating shortens life, and not just because overindulgence can lead to diseases such as diabetes. A diet that cuts food intake by up to 40%, known as calorie restriction, increases longevity in a variety of organisms and forestalls cancer, heart disease, and other late-life illnesses. Although some short-term studies suggest that calorie restriction provides metabolic benefits to people, nobody has confirmed that it also increases human life span. The closest researchers have come are two large, long-term studies of monkeys, and they conflict about whether meager rations increase longevity.

Even if calorie restriction could add years to our lives, almost no one can muster the willpower to eat so little day after day, year after year. An alternative that might be more, er, palatable is fasting, the temporary abstinence from food. Gerontological researcher Valter Longo of the University of Southern California in Los Angeles and colleagues have shown that fasting eases side effects of chemotherapy such as fatigue and weakness, and animal studies suggest that it produces health advantages similar to calorie restriction.

But hard-core fasting, in which people drink only water for days at a time, may be no easier than calorie restriction. “I’ve done it, and it was excruciating,” Longo says. For the new study he and his colleagues devised a less grueling diet that might still trigger the benefits of fasting. For two 4-day periods each month, middle-aged mice dined on low-protein, low-calorie chow. The rest of the month, they could nosh as much as they wanted.

The mice outlived their peers by an average of 3 months, a substantial amount for the rodents, and they displayed numerous signs of better health. As the researchers report online today in Cell Metabolism, the mice shed fat and were 45% less likely to fall victim to cancer. During their lean cuisine episodes, their level of blood sugar fell by 40% and the amount of insulin in the blood was 90% lower. And although brainpower usually declines with age, the mice retained more of their mental ability; they bested control animals in two kinds of memory tests, perhaps because they produced more new neurons in the hippocampus, a brain area crucial for memory.

Longo and colleagues also uncovered evidence that the regimen boosted the animals’ capacity to restore and replenish their tissues. “That’s the most exciting” finding, Longo says. For instance, regeneration of the liver was quicker in the fasting animals, and the balance of different types of cells in their blood was more youthful. The numbers of certain stem cells also soared in the dieting rodents.

To determine whether occasional austerity might have the same impact on people, the researchers whipped up a menu of energy bars, soups, teas, and chips. One day’s fare furnishes between 725 and 1090 calories. “It’s not like eating ravioli, but it is better than going without,” Longo says. (The average adult man in America needs about 2000 to 3000 calories daily; people following calorie restriction may limit themselves to as few as 1200 calories.)

Much like the mice, the volunteers in the study followed the diet for 5 days straight and then returned to their usual dining habits for the rest of the month. In their paper, the researchers report the results for the first group of 19 subjects to try this “fasting mimicking” regimen and for 19 controls.

Only three rounds of alternating between the diet and normal eating appeared to improve the participants’ physical condition, reducing blood glucose, trimming abdominal fat, and cutting levels of a protein associated with a higher risk of cardiovascular disease. Longo and colleagues also detected a slight rise in the abundance of some stem cells in the blood, suggesting that the diet might promote regeneration in humans. “We think that what the fasting mimicking diet does is rejuvenate,” Longo says.

Other researchers say the results of the study are encouraging. “This single dietary change can counteract all these variables of aging, and I think that’s very impressive,” says molecular biologist Christopher Hine of the Harvard School of Public Health in Boston. The study shows that cutting calories all the time may not be necessary, adds biochemist James Mitchell, also of the Harvard School of Public Health. “Intermittent periods can have lasting effects.”

The new diet may also be more practical. “Calorie restriction has failed miserably in human trials” because it’s so hard to stick to, says gerontologist Rafael de Cabo of the U.S. National Institute on Aging in Baltimore, Maryland, who leads one of the monkey studies of calorie restriction. A regimen like the researchers use “is achievable,” he says.

Longo and colleagues have already completed a larger clinical trial of the diet with more than 80 subjects. Fasting like the Buddha is dangerous, and even the fasting mimicking diet could be harmful for some people, such as diabetics, Longo notes. Researchers need to study how the regimen works, who might benefit, and who might be harmed by it, Mitchell notes. “There is a lot of information to figure out.”